Various attempts have been performed for applying polymeric sponges to living organism because of a good water absorption property thereof. Among them, sponges made of biodegradable polysaccharide are useful owing to a high affinity to the living organism, i.e., a good biocompatibility. However, many polysaccharides having such a good biocompatibility have a hydrophilicity and, therefore, tend to be easily decomposed in vivo. For this reason, polysaccharides used for the sponges are frequently insolubilized or converted into high-molecular ones in order to retard or prevent the degradation of the sponges in vivo, thereby obtaining biocompatible sponges.
For example, in Japanese Patent Application Laid-Open (KOKAI) No. 10-226732, there has been proposed the method for producing a polysaccharide sponge by freezing a polysaccharide solution, immersing the frozen solution in a water-miscible organic solvent containing a crosslinking agent to crosslink the polysaccharide, and then drying the crosslinked product to obtain a sponge.
However, in the above-mentioned method, since the obtained sponge still contains the unreacted crosslinking agent, it is required to subject the sponge to post-washing treatment. However, it may, be extremely difficult to wash a porous material such as sponges.